Jasper is a gemstone variety of quartz. Colors range through red, yellow, green or brown. Jasper is mentioned very early in Bible History as one of the twelve gems of the High Priest's breastplate, and in Prophecy, as in one of the foundations of the New Jerusalem.
"And the building of the wall of it was of jasper: and the city was pure gold"
The twelve precious stones in the High Priest's breastplate (the Levite high priest was actually just a prototype of the Savior - see High Priest to King of The World) signified the twelve tribes of Israel:
"And thou shalt make the breastplate of judgment with cunning work; after the work of the ephod thou shalt make it; of gold, of blue, and of purple, and of scarlet, and of fine twined linen, shalt thou make it.Foursquare it shall be being doubled; a span shall be the length thereof, and a span shall be the breadth thereof."
"And thou shalt set in it settings of stones, even four rows of stones: the first row shall be a sardius, a topaz, and a carbuncle: this shall be the first row. And the second row shall be an emerald, a sapphire, and a diamond. And the third row a ligure, an agate, and an amethyst. And the fourth row a beryl, and an onyx, and a jasper: they shall be set in gold in their enclosings."
"And the stones shall be with the names of the children of Israel, twelve, according to their names, like the engravings of a signet; every one with his name shall they be according to the twelve tribes." (Exodus 28:15-21 KJV)
The twelve foundations of gemstones in the New Jerusalem signify the twelve apostles. And by the way, note that the only reference to "pearly gates" in the Holy Bible are those that will be found on earth, in the yet-future New Jerusalem (see The City To Come):
"And the wall of the city had twelve foundations, and in them the names of the twelve apostles of the Lamb."
"And he that talked with me had a golden reed to measure the city, and the gates thereof, and the wall thereof. And the city lieth foursquare, and the length is as large as the breadth: and he measured the city with the reed, twelve thousand furlongs. The length and the breadth and the height of it are equal. And he measured the wall thereof, an hundred and forty and four cubits, according to the measure of a man, that is, of the angel."
"And the building of the wall of it was of jasper: and the city was pure gold, like unto clear glass. And the foundations of the wall of the city were garnished with all manner of precious stones. The first foundation was jasper; the second, sapphire; the third, a chalcedony; the fourth, an emerald; The fifth, sardonyx; the sixth, sardius; the seventh, chrysolyte; the eighth, beryl; the ninth, a topaz; the tenth, a chrysoprasus; the eleventh, a jacinth; the twelfth, an amethyst."
"And the twelve gates were twelve pearls: every several gate was of one pearl: and the street of the city was pure gold, as it were transparent glass." (Revelation 21:14-21 KJV)
Fact Finder: Is jasper mentioned in the description of the Throne of God?
Revelation 4:3 (see also The Throne Of God, From Heaven To Earth)